Mechanical waves are waves that require a medium. This means that they have to have some sort of matter to travel through. These waves travel when molecules in the medium collide with each other passing on energy. One example of a mechanical wave is sound. Sound can travel through air, water, or solids, but it can't travel through a vacuum. It needs the medium to help it travel. Other examples include water waves, seismic waves, and waves traveling through a spring.
Hi Kelly, I'm now 28 weeks pregnant with twins and I first started feeling them move when I was around 15/16 weeks pregnant but this is my second pregnancy. In my first pregnancy (not twins) I didn't feel any movement until I was 24 weeks pregnant. I think everyone feels their babies at different times so don't worry about anything.
Foetal movement: Feeling baby kick. All babies develop at different rates, but being able to feel the baby kick usually happens during the second trimester of pregnancy. For a first pregnancy, you may not feel your baby move until closer to 25 weeks. By the second pregnancy, some women start to feel movements as early as 13 weeks. You're more likely to feel baby move when you're in a quiet position, either sitting or lying down. Different mothers describe their baby's movements as butterflies, nervous twitches, or a tumbling motion.